1. Field of the Invention
The present invention relates to a strain sensor.
Priority is claimed on Japanese Patent Application No. 2013-100751, filed May 10, 2013, and Japanese Patent Application No. 2014-2044, filed Jan. 8, 2014, the content of which are incorporated herein by reference.
2. Description of Related Art
A strain sensor that detects strain is constituted so as to detect strain from the resistance change of a resistive body with respect to strain (extension and contraction). A metal or semiconductor is generally used as this resistive body. However, since the reversible amount of extendable and contractable deformation of a metal or semiconductor is small, the applications of a strain sensor are limited.
Therefore, a device using carbon nanotubes (CNT) as the resistive body has been proposed (refer to Japanese Unexamined Patent Application Publication No. 2003-227808). In this device, a CNT film or the like is used consisting of a plurality of CNTs that are oriented in a predetermined direction.
However, in the conventional device, since the CNT film is arranged in a state of contact with the outside air, problems arise in relation to the durability (service life) of the sensor function, such as the occurrence of abnormalities in the resistance change due to contamination of the CNT film by foreign substances and adhesion of moisture and floating gas to the CNTs, and the occurrence of falling off of the CNT film.
Also, in the case of the conventional device, although it is possible to increase the linearity of the resistance change, in addition to the problem of contamination of the CNT film by foreign substances, there is also a risk of CNTs shifting to a direction perpendicular to their direction of extension and contraction so that the CNTs make contact with each other, causing unforeseen resistance changes and response delays.